Geological Wonders Exposed by Satellite

By Rebecca Horne

Tassili n’Ajjer is a UNESCO World Heritage Site that covers 27,800 square miles in southeastern Algeria. NASA

Tassili n’Ajjer National Park in the Sahara Desert is a dry rocky plateau that rises above the surrounding sand. Tassili n’Ajjer, which translates to “Plateau of Rivers”, is a UNESCO World Heritage Site that covers 27,800 square miles in southeastern Algeria. Over billions of years, alternating wet and dry climates shaped these rocks. Deep ravines that are remnants of ancient rivers are cut into cliff faces along the plateau’s northern margin, where they once flowed off the plateau into nearby lakes. In drier periods, winds eroded the sandstones of the plateau into “stone forests,” and natural arches.

This image was made from multiple observations by the Landsat 7 satellite, using a combination of infrared, near-infrared and visible light to distinguish between the park’s various rock types. This means that sand appears in shades of yellow and tan, granite appears brick red, and blue areas are likely salts. As the patchwork colors show, the geology is complex. Humans have also modified the park’s rocks. From 10,000 BC to the first centuries of our era, successive peoples left many archaeological remains, habitations, burial mounds and enclosures which have yielded abundant lithic and ceramic artifacts. However, it is the rock art (engravings and paintings) that have made Tassili world famous as from 1933, the date of its discovery. Some 15,000 engravings have been identified to date. To encompass the intricacy of sites like Tassili n’Ajjer, the Ministry of Culture introduced a new category of protection for cultural and natural values: the cultural park – geographical locations in which cultural and natural values are interlinked.